1. Field of the Invention
The present invention relates to a liquid jet recording head and a liquid jet recording system incorporating such a liquid jet recording head.
2. Related Background Art.
Amongst various recording systems heretofore known, a non-impacting system referred to as an "ink jet recording system" is superior in that it enables high-speed recording on ordinary paper sheet without substantial noise and without requiring any specific fixing treatment.
Various proposals and improvements have been made with respect to this type of recording system. Some of these proposals and improvements have already been carried out commercially, while others are still in the course of being developed for practical use.
The ink jet recording system employs a recording liquid generally referred to as "ink liquid". Droplets of the recording liquid are made to fly by various methods towards the recording member such as a paper sheet so as to be deposited on the recording member, thereby recording the desired information.
The present applicant also has proposed a new recording system of ink jet type, as disclosed in German Patent Laid-Open No. 2,843,064. This new method relies upon the following principle. Namely, thermal pulses as information signals are delivered to the recording liquid contained by a chamber. As a result of the application of the thermal pulses, the ink generates vapor voids which in turn cause the ink to be contracted and pressurized so as to be discharged from the chamber. The thus discharged recording liquid is made to fly in the form of a droplet towards the recording member and is deposited on the latter so as to record the inputted information.
This system is easily adaptable to high-speed recording and color recording, because of the feasibility of providing a high-density multi-array arrangement. In addition, since this principle can be put into use by a simpler arrangement than a conventional one, the recording head as a whole can be made compact and mass-produced easily. It is to be noted also that, by making effective use of IC (integrated circuit) and microprocessing technologies which have made remarkable progress, the recording head can have a suitably large length. For these reasons, this new liquid jet recording system can enjoy a wide use.
This liquid jet recording system features a recording head which incorporates an electro-thermal transducer as means for forcing out the ink and forming droplets of the liquid.
In order to attain a highly efficient application of the heat energy to the liquid, as well as a high responsive behavior of the liquid with respect to the on-off control of the heat, it is considreed that the electro-thermal transducer is preferably provided in a heating region which communicates with the discharge port, so that it may directly contact the liquid.
The electro-thermal transducer is basically composed of a heat-generating resistance element which generates heat when supplied with electric power and a pair of electrodes through which the electric power is supplied to the resistance element.
This direct contact between the electro-thermal transducer and the recording liquid, however, suffers from the following disadvantages. Namely, the direct contact between the electro-thermal transducer and the liquid may cause leaking of electric current through the recording liquid, depending on the resistivity of the liquid. The electric current flowing in the liquid may cause electrolysis of the liquid. There is also a risk of reaction between the heat-generating resistance element and the liquid when the element is activated by the electric power supplied thereto. Such a reaction may lead to corrosion of the heat-generating element, resulting in a change in the resistivity and/or destruction of the heat-generating element. It is also possible that the surface of the heat-generating element will be mechanically eroded or the element cracked or broken by a mechanical impact caused when the vapor voids generated as a result of application of the electric power collapsed to be extinguished.
In order to obviate this problem, it has been proposed that a protective layer made of a material having a high resistance to acid such as SiO.sub.2 be formed on the surface of the heat-generating element which is made of an inorganic material superior in terms of the characteristics required for a heat-generating resistor, e.g., an alloy such as NiCr or borides of metals such as ZrB.sub.2 and HfB.sub.2. This protective layer is intended for preventing the heat-generating element from directly contacting the recording liquid, so as to improve the reliability and durability against repeated use, thereby obviating the above-described problems.
The liquid jet recording system having a recording head incorporating this improved electro-thermal transducer can be used satisfactorily in terms of both resistance to acid and durability, when a liquid having a comparatively low electric conductivity, such as a liquid prepared by using water or an alcohol as the solvent, is used as the colored recording liquid. This recording system, however, has often failed to provide satisfactory durability and stability against secular change when used together with a recording liquid having a large content of Na ions and, hence, high electric conductivity. For this reason, it has only been possible to use this recording system with selected recording liquids and, therefore, it has not been suitable for use with multi-color or natural color recording.
As explained above, the reliability and durability of the electro-thermal transducer would be improved by providing a protective layer on the heat-generating element. Actually, however, it is very difficult to form such a protective layer on a mass-production scale with a high degree of reproducibility, and protective layers so produced tend to have defects which undesirably permit the recording liquid to penetrate into the electro-thermal transducer towards the heat-generating element.
This problem is particularly serious in the case of an arrangement known as "high-density multi-orifice" in which a liquid passage or nozzle is provided with a multiplicity of heating sections arranged at a high density. Namely, such an arrangement requires that numerous electro-thermal transducers, corresponding in number to the number of the liquid nozzles, are formed at one time. Therefore, any failure in any of the electro-thermal transducers attributable to a defect in the protective layer causes a serious problem from the view point of yield of the recording system, as well as the production cost. In addition, the protective layer tends to deteriorate the thermal response characteristic, and also the heat generating characteristic in response to inputted electric signals.
Under these circumstances, there is an increasing demand for development of a liquid jet type recording system which employs an electro-thermal transducer having no protective layer so that the heat-generating element is directly exposed to the recording liquid, the electro-thermal transducer yet being highly resistant to heat, acid, mechanical impact and electro-chemical reaction, while exhibiting a superior thermal response characteristic.